1. Field of the Invention
This invention relates to a catalyst and method for preparing lower aliphatic alcohols. More particularly, this invention relates to the production of a mixture of lower aliphatic alcohols characterized by containing, in addition to methanol, a substantial proportion of alcohols having from 2 to 6 carbon atoms.
2. Description of Background Art
Lower aliphatic alcohols have been proposed as fuel extenders or as replacements for gasoline for fueling internal combustion engines. Certain mixtures of lower aliphatic alcohols have the EPA approval for use and are currently being marketed in the United States. The lower aliphatic alcohols can be produced from domestically available non-petroleum sources. Therefore, their use in fuels would serve to lessen the dependence of the nation on imported petroleum and petroleum products.
Hydrogen and carbon monoxide, or a synthesis gas mixture of hydrogen and carbon monoxide, can be reacted to form lower aliphatic alcohols. The synthesis gas feed stream can be produced from non-petroleum sources, such as coal, biomass or other hydrocarbonaceous materials. The synthesis gas mixture itself is produced in a partial oxidation reaction of the hydrocarbonaceous material in commercially available processes, such as coal gasification.
Numerous catalysts and catalytic methods have been studied in attempts to provide a viable method for the production of aliphatic alcohols from synthesis gas or from a mixture of hydrogen and carbon monoxide. Heretofore, the emphasis has been primarily directed to the production of methanol. In contrast, the present process is directed to a method for producing an alcohol mixture containing, in addition to methanol, a substantial amount of aliphatic alcohols having 2 or more (preferably between 2 to 6) carbon atoms.
One of the shortcomings associated with the known methods of making alcohols from synthesis gas is the substantial amount of hydrocarbons that are coproduced. The hydrocarbons so produced represent a major loss in carbon utilization. Surprisingly, under selected reaction conditions, the catalyst and method of the present invention result in the production of a significant fraction of aliphatic alcohols having from 2 to 6 carbon atoms, without the substantial coproduction of undesirable hydrocarbons.
U.S. Pat. No. 4,096,164 discloses a process for reacting hydrogen and carbon monoxide in the presence of a solid catalyst comprising rhodium with molybdenum or tungsten to produce two carbon atom oxygenated hydrocarbons in which ethanol is the major component. This disclosure is incorporated herein by reference.
U.S. Pat. No. 4,380,589 discloses a Fischer-Tropsch process for producing hydrocarbons with improved selectivity to C.sub.2 -C.sub.4 olefins by contacting hydrogen and carbon monoxide in the presence of a catalyst. The catalyst disclosed comprises molybdenum, a promoter comprising an alkali or alkaline earth metal and a binder comprising an iron-containing calcium aluminate cement.
U.S. Pat. No. 4,607,055 discloses a process for producing lower aliphatic alcohols from a mixture of carbon monoxide and hydrogen in the presence of a catalyst comprising molydbdenum; a metal from the group consisting of cobalt, iron and nickel; and silver. The catalyst is modified by the addition of a promoter from the class consisting of potassium, cesium and rubidium. This disclosure is incorporated herein by reference.
U.S. Pat. No. 4,661,525 discloses a process for producing lower aliphatic alcohols from a mixture of carbon monoxide and hydrogen in the presence of a catalyst comprising molybdenum and a metal selected from the group consisting of cobalt, iron and nickel which has been promoted by an alkali metal selected from the group consisting of potassium, cesium and rubidium. This disclosure is incorporated herein by reference.
EPA No. 119609 discloses a process for producing alcohols from synthesis gas using a catalyst containing molybdenum with tungsten, rhenium and an alkali metal. This disclosure is incorporated herein by reference. E.P. No. 79132 discloses a similar process in which the catalyst contains rhenium, molybdenum and potassium.
Co-assigned application Serial No. 939,392 filed on Dec. 12, 1986 is directed to a process for producing lower aliphatic alcohols from a mixture of carbon monoxide and hydrogen in the presence of a catalyst comprising rhodium, molybdenum and an alkali metal. This disclosure is incorporated herein by reference.
Previous catalytic methods have been notably effective for converting carbon monoxide and hydrogen feedstocks into hydrocarbons or methanol, but none have been particularly selective for providing, in addition to methanol, a substantial yield of a lower aliphatic alcohol mixture at a moderate reaction temperature and reaction pressure.